Reciprocating piston type internal combustion engines whether two or four stroke, suffer from two principal disadvantages. In the two-stroke engine, the intake air/fuel mixture is mixed with the exhaust gases remaining in the cylinder or is partially blown out with them and in the four-stroke engine, energy is wasted in separate exhaust and intake strokes as well as in the valve operating system. Furthermore, in both types of engine, the pistons have to be accelerated to a maximum speed and then slowed down and stopped both at the upper and lower ends of the piston which causes considerable wear to the components making up the engine.
Rotary engines solve these problems in general, but suffer also from disadvantages, the principal one of which is balance and difficulty in sealing and lubrication.